1. Field of the Invention
The present invention relates to devices and methods of improving a patient's vision. In particular, the invention relates to improving vision of a patient by placing a corrective ocular device between an epithelium of the patient's eye and the stroma of the cornea of the patient's eye. The corrective ocular device may be a lens, including a corneal onlay. The corrective ocular device may have a preformed epithelial cell layer secured over the device when placed on an eye of a patient. The preformed epithelial cell layer may be synthesized in vitro or the preformed epithelial cell layer may include at least a portion of the patient's corneal epithelium.
2. Description of Related Art
The cornea of the human eye provides between approximately 60 and 70 percent of the focusing power of the eye. As understood in the art, lenses may be placed in proximity of the cornea to augment the focusing capabilities of the eye. Examples of vision correction lenses include corneal inlays, which are implanted within the cornea, corneal onlays, which are placed over the cornea after the epithelium has been removed, and contact lenses, which are placed over the corneal epithelium. Corneal onlays differ from contact lenses in that corneal onlays are covered by an epithelial cell layer compared to contact lenses that are placed over the corneal epithelium.
Because corneal onlays are placed on a deepithelialized cornea, it is necessary for the epithelium to be replaced over the onlay to prevent damage and infection to the eye. Epithelial cells develop from the corneal limbus and migrate over the eye. Unfortunately, many materials from which existing corneal onlays are manufactured from do not effectively promote epithelial cell growth and migration over the onlay.
Some attempts have been made to create corneal onlays that attempt to improve the migration of epithelial cells over the onlay. For example, U.S. Pat. No. 5,171,318 discloses the use of fibronectin disposed over the surface of an onlay to facilitate cell migration over the onlay and attachment to the onlay. U.S. Pat. No. 5,713,957 discloses non-biodegradable non-hydrogel corneal onlays having large pores in the periphery of the onlay, which are intended to facilitate securement of the onlay to the eye by permitting cells to grow through the pores. U.S. Pat. No. 5,836,313 discloses a composite hydrogel corneal onlay that comprises a layer of corneal tissue or collagen to improve cell migration over the corneal onlay. U.S. Pat. No. 5,994,133 discloses corneal onlays fabricated from various polymers that permit epithelial cells to migrate over the onlay. U.S. Patent Publication No. US 2001/0047203 A1 discloses corneal onlays with surface indentations that supports attachment and migration of the epithelial cells over the onlay. PCT Publication No. WO 02/06883 discloses a corneal onlay derived from donor corneal tissue. In addition, WO 02/06883 appears to disclose the use of an epithelial cell layer placed over the onlay; the epithelial cell layer may be obtained from donor tissue, such as fetal or embryonic tissue, or autologous tissue biopsies of corneal epithelial cells. The corneal onlays which require epithelial cells to migrate over the onlay surface fail to provide satisfactory coverage of the onlay with the epithelium. For example, when epithelial cells are required to migrate over corneal onlays, the epithelial cells may not differentiate fully. Moreover, as the epithelial cells migrate, there may be a tendency for the epithelium to grow under the corneal onlay placed over the eye and cause the onlay to be dislodged or encapsulated. In addition, the recovery time for the epithelial cells to grow and migrate over the onlay is prohibitive and contributes to the undesirability of these approaches.
While WO 02/06883 discloses the use of cultured epithelial cells to create a layer of epithelium that may be used to cover a corneal onlay, it does not disclose using cultured stem cells to create a layer of epithelium. Indeed, culturing stem cells to create a corneal epithelium has only recently been explored (e.g., see Han et al., “A fibrin-based bioengineered ocular surface with human corneal epithelial stem cells”, Cornea, 21(5): 505-510 (2002); and U.S. Patent Publication No. US 2002/0039788 A1). These references disclose culturing corneal epithelial stem cells to repair damaged ocular surfaces. Although complications did not appear to be too significant for correcting damaged ocular surfaces, it was noted that it may be problematic to use cultured stem cells with corrective lenses.